Low-amplitude coherently coupled spatial soliton pairs due to both the linear and quadratic electro-optic effects

A comprehensive study of coherent coupling of lowamplitude spatial solitons that copropagate in biased photorefractive crystals with both the linear and quadratic electrooptic effects was presented. Our results were shown that coherently coupled brightbright and darkdark spatial soliton pairs in the low amplitude regime could be formed under appropriate conditions. The evolution equations, analytic solutions and the expressions of soliton pair widths of these lowamplitude coherently coupled spatial soliton pairs were obtained. It was proven that the existence, property and propagation of these soliton pairs due to coeffects of both the linear and quadratic electrooptic effects was greatly influenced by the photorefractive effects which could be enhanced, weakened or even counteracted because of the interaction of these two electrooptic effects. Moreover, the effects of three physical factors, i.e., the initial phase difference between two incident coherent beams, the intensity ratio and various external bias field on the existence conditions, properties of these lowamplitude coherently coupled soliton pairs have been discussed in detail. Finally, the selfdeflection of lowamplitude brightbright soliton pairs had also been investigated by means of perturbation procedure.